It is well known in the electronic art that many solid state devices generate a considerable amount of heat which must be dissipated away from the solid state device in order to prevent failures. In order to assist with this heat dissipation or "heat sinking," many of these solid state devices are manufactured integrally mounted to a substantially flat metal plate, a portion of which extends beyond the device's main body, forming a metal tab-like construction which incorporates a through hole near its exposed end. Generally, the electrodes of the solid state device protrude in a direction opposite from the direction of the exposed apertured metal tab.
In mounting these solid state devices, the exposed apertured metal tab is employed with fastening means for directly anchoring the solid state device to a holding plate, constructed for absorbing and dissipating the heat generated by the solid state device. This type of construction and mounting system is generally employed throughout the industry in the manufacture of a wide variety of products. In U.S. Pat. No. 3,641,474, this conventional structure is discussed and clearly shown. In addition to this conventional anchoring system, this patent also employs restraining blocks for preventing the rotation of the solid state device about the axis of the anchoring screw when the solid state device is being affixed to the heat sinking plate.
Although this conventional system does provide suitable heat sinking capability for the heat generated by these solid state devices, the direct fastening of the apertured metal tab to a mounting plate creates additional problems which have heretofor gone completely unresolved. This major problem is controlling the spacing between the electrically live apertured metal tab of the solid state device and the metal heat sinking plate.
It is well known that where electrically live parts are employed in close proximity to grounded or floating conductive parts, the distance or "spacing" between the live parts and the grounded or floating conductive parts is an important design perimeter which must comply with minimum acceptable standards in order to assure the safety and reliability of the system. The minimum spacing is required to avoid arcing from live parts to the grounded parts and shorting of live parts to grounded or floating conductive parts. In addition the minimum spacing also prevents potential fire and safety hazards from occuring due to electrical leakage current flowing between the live parts and adjacent grounded parts as a result of contamination of surfaces between these parts.
In determining compliance of standards for minimum acceptable spacing, both the "through air" and "over surface" spacing must be considered. As a result, in conventional mounting of solid state devices to suitable heat sinking surfaces, insulators are employed to comply with these minimum acceptable standards for through air and over surface spacings.
As shown in U.S. Pat. No. 3,641,474, compliance with these standards requires the use of a dielectric sheet between the semi-conductor and the heat sinking plate, as well as an insulating bushing passing through the apertured metal tab in order to achieve sufficient insulation of the anchoring screw from the heat sinking plate. As is readily apparent to one skilled in this art, this construction is extremely disadvantageous since a large number of small hand assembled parts is required.
Another problem which exists with these prior art mounting systems is the difficulty of accommodating the varying dimensions of the necessary parts. Since these parts are all mass produced, the tolerance on the thickness of items such as the metal tab or the thickness of the insulating bushings are not closely controlled. As a result, the thickness of one metal tab or bushing can be very different from the next.
These variations become a critical problem when these devices must be mounted to the heat sink plate within a specific tolerance to prevent electrical conduction to the heat sink plate. When the allowed tolerance is small, these variations can present time consuming and costly problems.
Therefore, it is the principle object of the present invention to provide a solid state device mounting assembly that securely maintains the solid state device in position without employing fastening means extending through the solid state device.
Another object of the present invention is to provide a solid state device mounting assembly having the characteristic features defined above which is capable of simultaneously holding a plurality of solid state devices in a single easily assembled module.
Another object of the present invention is to provide a solid state device mounting assembly having the characteristic features defined above which is capable of transferring the heat generated by the solid state devices to a suitable heat dissipating surface.
Another object of the present invention is to provide a solid state device mounting and heat dissipating assembly having the characteristic features described above which is both easy and inexpensive to manufacture.
Another object of the present invention is to provide a solid state device mounting and heat dissipating assembly having the characteristic features described above which is quickly and easily assembled and installed in an operating system.
Other more specific objects will in part be obvious and will in part appear hereinafter.